Pruning shrubs is all about timing

Shrub pruning is one outdoor job that is often done just before plant growth begins again in the spring, so here are a few tips to help guide your pruning efforts.

Deciduous shrubs fit into two groups: shrubs that flower in the spring on wood produced last year and shrubs that flower during the summer on current season’s (new) growth.

Spring flowering shrubs should not be pruned until immediately after flowering.  Pruning earlier will not harm the plant’s health, but the flowering display will be reduced. Examples of these types of plants include forsythia, lilac, quince and mock orange, serviceberry, and viburnum.

Shrubs that bloom on current season’s growth or that do not produce desirable flowers are best pruned now in late winter.   Examples include caryopteris, shrub roses, pyracantha, rose of Sharon, spirea, butterfly bush, vitex, and more.

An easy way to remember this is to use the rule of June 1st. If a shrub blooms before June 1st, plan to prune it after it flowers and if the shrub blooms after June 1st, plan to prune it it late winter or early spring.

There are three basic methods used in pruning shrubs: thinning, heading back and rejuvenating.

Thinning or renewal pruning is used to eliminate branches from a shrub that is too dense. The objective is to remove one-third of the oldest stems to the ground each year, which in turn stimulates new (flowering) growth from the base of the shrub. 

Heading back is done by removing the end of a branch by cutting it back to a bud and is used for either reducing height or keeping a shrub to a compact size. When cutting back to a bud choose a bud that is pointing in the direction you wish new growth to go.

Rejuvenation is the most severe type of pruning and may be used on multi-stem shrubs that have become too large or have too many old branches to justify saving the younger canes. Every stem on the plant is cut back to a 5- to 6-inch stub. This is not recommended for all shrubs but it does work well for many including lilac, dogwood, privet, rose of Sharon, elderberry, honeysuckle, spirea, forsythia, pyracantha, ninebark, mock orange, shrub roses and flowering quince. Note that with rejuvenation pruning there may be no flowers for up to two years on some shrubs.

Remember that evergreen shrubs cannot be rejuvenation pruned and typically differ in their pruning requirements from deciduous shrubs.  Many evergreen shrubs do not regrow like deciduous plants and must be pruned more carefully.

Examples of thinning (renewal) and rejuvenation pruning: